This is merely a historical archive of years 2008-2021, before the migration to mailman3.
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Jay Salsburg jsalsburg at bellsouth.netHello Michel The fact about Cooling Electronics comes down to how much benefit is obtained by lowering the chip temperature. While lowering the temperature of CCDs contributes to lowering the Chip's Dark Current and single pixel artifacts, the benefits to reducing noise of Low Noise Radio Frequency Amplifiers is not very effective, at least from what a Peltier cooler would provide. Reducing noise in RF Amps will only be useful if you can reduce the "System Noise Temperature" (in Kelvin) by a factor of 4, resulting in doubling the effective communication range (number of Light Years). Examples of Cooling a GaAs PHEMT preamp with a noise temp of 50K at Room Ambient, with Dry Ice might at the most, reduce its noise by 35%; only a small improvement. However, the Antenna noise, plus Sky noise, plus Earth noise is the source of much of the unwanted noise, not the Amplifier hence the advantage of Space-based Receivers. So cooling an LNA with Dry Ice plus the unavoidable environmental noise provides only an 8% improvement. Cooling with a Peltier device or Dry Ice, while providing some benefit, is not worth the trouble. Cryogenic cooling provides a more desired effect. Placing a Cryogenic LNA (Liquid Helium) in front of the Tuner will definitely increase your Light Years, however, this technique is logistically complex and expensive, but possible. The obvious direction is toward an Array. This provides a solution to reduce noise through Signal Processing, with the down side of needing many more receivers and physical space for the Array. -----Original Message----- From: osmocom-sdr-bounces at lists.osmocom.org [mailto:osmocom-sdr-bounces at lists.osmocom.org] On Behalf Of Michel Pelletier Sent: Sunday, October 21, 2012 9:13 PM To: Jay Salsburg Cc: osmocom-sdr at lists.osmocom.org Subject: Re: Beginner question about rtlsdr On Sun, Oct 21, 2012 at 7:00 PM, Jay Salsburg <jsalsburg at bellsouth.net> wrote: > Hello Michel > > OK, I see you are way ahead of me. However, I have some experience > using these TV Dongles, they have pitfalls. Number one is its > frequency Accuracy, out-of-the-box; needs calibration. Another is that > its frequency accuracy drifts over time and from the Ambient > temperature necessitating periodic offset calibration. While it is > possible to create a compensation cure for frequency drift vs. > temperature, it may be far more prudent to place the Dongle in a > temperature controlled enclosure (50C Heater) keeping it above the > ambient to help prevent drift, in your case, the all too important > Temperature related Phase Shift. I have thought of disconnecting the > Dongle's Crystal and placing it in a Crystal Oven, but I have not > tried that. The Entire Dongle is small enough to place it in a temperature controlled enclosure which also keeps it dry. Interesting! I was actually considering going the other way, and putting the radio in a Peltier cooled enclosure, but that was based only on my experience with cooling digital cameras for astrophotography purposes to lower noise. I just instinctively figured that lower temperatures would equate to lower noise in a radio receiver as well, but I have no experience with the kind of accuracy drift or phase shift you're talking about. Well, this is definitely something I will keep in mind when I try to capture my first baseline. :) -Michel ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2741 / Virus Database: 2614/5846 - Release Date: 10/21/12